"For [More], as for Thomas Aquinas before him, the human conscience was not an autonomous lawgiver. Rather, a man's conscience was his belief, true or false, about the law made by God. To act against conscience was always wrong, because it was acting against what one believed to be God's law. But to act in accordance with conscience was not necessarily right; for one's conscience might be an erroneous opinion. One had a duty to inform one's conscience correctly; perhaps by consulting the Scriptures, or the writings of the Saints, or the authoritative doctrines of the Church. . . . The only case where a mistaken conscience would excuse from wrongdoing would be where the moral issue in question was a debatable one, where there was a division of opinion among saints and sacred writers."
Anthony Kenny, Thomas More, Past masters (Oxford: Oxford University Press, 1983), 94.